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Tuesday, June 11, 2013

Measure Quantum Motions of 1 Femtometer

The femtometre (symbol fm) is an SI unit of length equal to 10−15metres. This distance can also be called fermi and was so named in honour of Enrico Fermi and is often encountered in nuclear physics as a characteristic of this scale.

Mechanical systems are ideal candidates for studying quantum behavior of macroscopic objects. To this end, a mechanical resonator has to be cooled to its ground state and its position has to be measured with great accuracy. Currently, various routes to reach these goals are being explored. In this review, we discuss diﬀerent techniques for sensitive position detection and we give an overview of the cooling techniques that are being employed. The latter include sideband cooling and active feedback cooling. The basic concepts that are important when measuring on mechanical systems with high accuracy and/or at very low temperatures, such as thermal and quantum noise, linear response theory, and backaction, are explained. From this, the quantum limit on linear position detection is obtained and the sensitivities that have been achieved in recent opto and nanoelectromechanical experiments are compared to this limit. The mechanical resonators that are used in the experiments range from meter-sized gravitational wave detectors to nanomechanical systems that can only be read out using mesoscopic devices such as single-electron transistors or superconducting quantum interference devices. A special class of nanomechanical systems are bottom-up fabricated carbon-based devices, which have very high frequencies and yet a large zero-point motion, making them ideal for reaching the quantum regime. The mechanics of some of the diﬀerent mechanical systems at the nanoscale is studied. We conclude this review with an outlook of how state-of-the-art mechanical resonators can be improved to study quantum mechanics

Quantum Nanomechanics is the emerging ﬁeld which pertains to the mechanical behavior of nanoscale systems in the quantum domain. Unlike the conventional studies of vibration of molecules and phonons in solids, quantum nanomechanics is deﬁned as the quantum behavior of the entire mechanical structure, including all of its constituents—the atoms, the molecules, the ions, the electrons as well as other excitations. The relevant degrees of freedom of the system are described by macroscopic variables and quantum mechanics in these variables is the essential aspect of quantum nanomechanics. In spite of its obvious importance, however, quantum nanomechanics still awaits proper and complete physical realization.

In this article, I provide a conceptual framework for deﬁning quantum nanomechanical systems and their characteristic behaviors, and chart out possible avenues for the experimental realization of bona ﬁde quantum nanomechanical systems.